Why not to use USB external drives in an array?

[abyzek]

I see almost all users shucking their external usb drives and directly connecting them using SATA.

What is the disadvantage of directly using the external drives connected as USB (other than speed)?

 

I have 4x 8TB drives which are all in USB 3.0 enclosures. (2x Seagate Backup Plus Hub and 2x WD Easystore)

I was planning to use 3x as array disks and 1x as Parity (mainly as a media server).

 

Enclosure space is not a constraint for me so should I really shuck these drive?

 

[JonathanM]

USB is notorious for random disconnects, which kicks the drive out of the array. Also, the USB-SATA interface may introduce differences in absolute size, or other abnormalities like non-unique serial number returns or several other issues. Smart reports, and the ability to track drive health may be limited. Cooling can be a challenge.

 

Some drives work better than others as USB, but on the whole it's a recipe for disaster when you depend on all drives to work perfectly 100% of the time.

[trurl]

38 minutes ago, jonathanm said:

you depend on all drives to work perfectly 100% of the time.

And just in case you don't know how parity works, every bit of parity PLUS ALL other disks in the array must be read reliably in order to reliably rebuild a missing disk.

[limetech]

That said... doesn't hurt to try it.  Depending on h/w it might work out ok for you, unfortunately hard to tell in advance.

[limetech]

Though here is a good example of what can happen:

 

[captain_video]

External drives have really poor cooling as they are strictly passive and placed in a plastic enclosure that does not transmit heat.  They're also running off a wall wart AC adapter instead of a well regulated power supply.  I use external drives in my unRAID array almost exclusively, but I pull them from the enclosures first.  The drives used in external enclosures are the same as the desktop drives that you typically pay more for and have a longer warranty.  The warranty is shorter for external drives because they're not expected to last as long for the very reasons I just mentioned -  poorly regulated power and poor ventilation.  If you pull them from the enclosures and mount them in a server or desktop case they will more than likely last as long as their desktop counterparts.  Of course, pulling them from the enclosures voids the warranty, but doing so almost guarantees that they'll last longer than the warranty period anyway.